Vehicles include: (i) engine vehicles that use an engine as a travel driving source and (ii) electromotive vehicles that use an electric motor as a travel driving source. The electromotive vehicles include electric vehicles (EV) and hybrid electric vehicles (HEV).
A driver of an engine vehicle may sense a driving force of the vehicle from an engine sound in addition to an engine speed value indicated by a tachometer. Thus, the driver sensuously determines a time when a driving force corresponding to various kinds of starts are generated and starts the vehicle. The various kinds of start include, for example, a slow start, a backward start, and an uneven-surface start.
In the electromotive vehicle, a power meter that indicates the amount of power output to the motor is provided instead of a tachometer. However, because the motor is silent, it is difficult for a driver to aurally sense the driving force of the vehicle and to sensuously determine a time when a driving force corresponding to various kinds of starts are generated. Thus, the driver cannot sensuously determine how much driving force to be generated for starting the electromotive vehicle, and the driver may feel anxious.
Techniques for generating an imitative sound so that a driver of an electromotive vehicle can aurally sense a driving force of the vehicle are suggested. For example, JP-A-2005-31606 discloses a technique that plays an imitative sound of an engine sound in conjunction with driving of a vehicle. JP-A-11-288291 discloses a technique that plays an imitative sound of an engine sound in accordance with a rotation amount of a motor in an electric vehicle. JP-A-2001-283363 discloses a technique that generates an exhaust sound of an engine in accordance with a rotation amount of a tachometer or an amount of accelerator pedal operation in a hybrid electric vehicle.
However, even when the imitative sound of the engine sound is generated in accordance with driving of the vehicle as described above, a driver who is unfamiliar with an electromotive vehicle that generates the imitative sound of the engine sound may not judge how much sound volume of the imitative sound corresponds to an amount of driving force. Thus, even if the imitative sound of the engine sound is generated in accordance with driving, there is a possibility that the driver cannot sensuously determine how much driving force should be generated for starting the electromotive vehicle and the driver feels anxious.
Because a driver takes time to empirically learn how much sound volume of the imitative sound corresponds to an amount of driving force, the feeling of anxiety cannot be relieved easily.